This invention relates to metal cutting apparatus and, more particularily to a control means for the knee of a metal cutting apparatus.
Metal cutting machines, or machining centers, typically include a table on which the work piece is positioned and means for moving the table along a plurality of axes so as to allow the milling head to selectively engage the work piece. Some machines provide only an X and Y axis capability; that is, a capability only along the horizontal axes. Other machines provide an additional capability along the Z, or vertical, axis. The Z capablility is normally provided by one of two arrangements. In one arrangement, the table is movable only along the X and Y, or horizontal, axis, and the milling head is movable along the Z, or vertical, axis. In the other arrangement, and more typically, the table is moved along all three axes with the vertical movement of the table provided by a knee member positioned beneath the table and mounted for movement on a vertical slideway. Typically, the vertical movement of the knee member, and thereby the table, is provided by a nut and lead screw arrangement with the lead screw threading into a fixed nut carried by the support base of the machine and extending upwardly into the knee where is is journaled by bearing structure provided within the knee and where it is engaged by a drive mechanism housed within the knee. The drive mechanism includes a motor and either a gear drive assembly or a belt and pulley assembly. While this arrangement is in commom usage and is generally satisfactory, the mechanism providing the Z axis capability is built into the knee of the machine and is therefore dedicated to that single machine. Accordingly, in shops employing a plurality of milling machines, each machine must have its own Z axis capability even though that capability may only be required for selected jobs. The recited arrangement, with the bearing structure for the screw and the drive mechanism for the screw housed within the knee, also provides a very heavy knee structure with the result that the mass moving on the vertical slideway during Z axis cutting operations is very high.